Combined still and coil cracking



Jan. 26, 1937. F. A. HOWARD 2,068,856

, COMBINED STILL AND COIL CRACKING Filed July 25, 1929 ATTORNEY PatentedJan. 26, 1937 UNITED STATES PATENT OFFICE Frank A. Howard, Elizabeth, N.J., assignor to Standard Oil Development Company, a corporation ofDelaware Application July 25, 1929, Serial No. 380,783

2 Claims.

This invention relates to improvements in combined still and coilcracking of hydrocarbon oil, particularly that type in which a hotproduct from the coil is used to heat the oil in the still.

A principal object of the present invention is to provide an improvedcyclic circulation including coil, still and fractionation means. Aclean circulation is secured by removing tar in an expansion zone. Heatfrom the cracked product is imparted to the oil in the still by indirectheat exchange.

The invention will be fully understood from the following descriptionread in connection with the accompanying drawing in which the figure isa diagrammatic side elevation of preferred equipment.

Referring to the drawing, the equipment comprises a cracking coil Ilocated in a furnace setting 2 and discharging through line 3 having apressure control valve 3a into the lower portion of a vapor separator 4.Oil is passed into the system through a line 21, subsequently described.A line 5, controlled by a valve 6, permits the discharge of tar from theseparator.

Vapors from the separator 4 are conducted through line 1 and valve 8into the lower portion of a bubble tower III, which is provided with theusual bell caps II, down-flow pipes I2 and top cooling coil I3. Vaporsissuing from the bubble tower pass through a line I4 to a condensingcoil I5 and receiving drum I6. A distillate outlet I! and a gas outletI8 communicate with the 'drum. Valves I9 and 20 are provided in theseoutlets respectively. A pressure control valve 2I is provided in line I4between condenser I5 and tower Ill.

A still 25 is provided intermediate cracking coil I and separator 4 withthe line 3 passing therethrough whereby the contents of the still can beheated by the hot oil passing through the line 3. This line can bemanifolded or coiled so as to secure more extensive contact surface.

The still is preferably heavily lagged and is set over a furnace 25a.Vapors from the still are passed into the bubble tower through the line26 in which there is a pressure control valve 260.. Feed oil, togetherwith the heavier constituents condensed from the vaporous product in thebubble tower are introduced into the still through a line 30. A spreaderplate 30a is preferably provided to distribute the oil. A valve 3| isprovided in line 30. A line 32 connects line 30 thru valve 32a and pump33 with cracking coil I, for the introduction of feed oil and condensateinto the cracking coil. A line 34 communicates with the bottom of still25 and the line 32. A valve 35 is provided in line 34. The still bottomscan be conducted from still 25 through lines 34 and 32 into the crackingcoil I. A line 36 connects line 21 with cracking coil I and permits ofthe 5 introduction of fresh feed oil directly into the cracking coil. Avalve 3'! is provided in the line 36.

In operating the equipment, feed oil such as gas oil or the like isintroduced through line 21, bubble tower I0 and lines 30 and 32 intocracking coil I and thence into separator 4. The oil is subjected to atemperature of approximately 850-900 F. inthe cracking coil. Taraccumulating in the separator 4 is withdrawn through the line 5. Thevapors are withdrawn from the separator through line 1 into the bubbletower I0 Where they are rectified and in part condensed by the feed oil,the lighter ends thereof being simultaneously vaporized. The rectifiedvapors are withdrawn and condensed toform end products of fixed gas andcracked distillate.

The feed oil, together with the heavier constituents obtained from thevapors in the bubble tower, are subjected in the still to temperaturesapproximating 775 to 800 F., whereby additional cracking of the oil isobtained. Some or all of the heat used for distillation is obtained fromthe indirect heat exchange effected by the highly heated oil passingthrough line 3.

The oil is preferably maintained under a pressure of approximately 450#per sq. in. while passing through the cracking coil and separator and apressure of approximately 200 to 400# per sq. in. is preferablymaintained in the still and tower. A lower pressure than 450 pounds persquare inch can be maintained in the separator and some of theadvantages of the invention will be retained. Bottoms are continuouslywithdrawn from the still through pipes 34 and 32 by means of pump 40 33or otherwise and pass through the cracking coil I where they are raisedin temperature approximately to 125 F. thereby vaporizing approximately60 to of the bottoms when the pressure is reduced as in the separator 4.The 45 highly heated oil and vapors passing through the line 3 supplythe heat for cracking and vaporizing the oil in the still, and alsooffset the heat lost by radiation from the still, and drop intemperature approximately 75 to as a consequence thereof. Heat fromother sources may be also supplied to the still, if required.

Numerous changes and alternative arrangements may be made within thescope of the ap- 55 pended claims in which it is the intention to claimall novelty inherent in the invention as broadly as the prior artpermits.

I claim:

1. The method of cracking petroleum which comprises introducing saidpetroleum into a fractionating zone, passing it counter-currently insaid zone to vaporous cracking products whereby said petroleum ispartially stripped, introducing the residual petroleum into a crackingand distillation zone where it is subjected to conditions suitable forlimited cracking and distillation, removing vaporous products from thiszone, passing the residual petroleum from this zone to an elongatednarrow heating zone in which it is subjected to more severe crackingconditions, conducting the total cracked eflluent directly through thesaid cracking and distillation zone in indirect heat exchange relationthereto without permitting any of said cracked effluent to come incontact with products undergoing cracking in said cracking anddistilling zone, passing said cracked effluent to a separator,withdrawing tar from said separator and rejecting it from the system andpassing vaporous products to said fractionating zone.

2. The method of cracking petroleum, which comprises the crackingdistillation of the petroleum at temperature and pressure of the orderof 775 to 800 F. and 200 to 400 pounds per square inch, taking ofivapors, Withdrawing unvaporized residues and heating them to crackingtemperature and pressure of the order of 850 to 900 F. and above 400pounds per square inch, passing the heated residues while at crackingtemperature in indirect heat exchange relationship with the oilundergoing cracking distillation to heat said oil, separating theresidues into vapors and tar in a separation zone maintained under apressure between 200 and 450 pounds per square inch, withdrawing thetar, stripping light fractions from the petroleum passing to thecracking distillation, by contact with vapors from the crackingdistillation and the separation Zone and supplying additional heat tothe oil undergoing cracking distillation from a source independent ofthe products of cracking.

FRANK A. HOWARD.

